The present invention relates to a position correcting method and apparatus for an ink fountain key that correct the home position/present position of an ink fountain key in a printing press when adjusting the opening amount (position) of the ink fountain key.
FIG. 19 shows the schematic arrangement of an ink supply unit in each printing unit of a rotary printing press. Referring to FIG. 19, the ink supply unit has an ink fountain 1, an ink 2 stored in the ink fountain 1, an ink fountain roller 3, a plurality of ink fountain keys 4 aligned in the axial direction of the ink fountain roller 3, an ink ductor roller 5, an ink roller group 6, a plate 7, and a plate cylinder 8.
FIG. 20 shows the outline of a general four-color rotary printing press. Referring to FIG. 20, printing units 9-1 to 9-4 perform printing in units of colors. The ink supply unit shown in FIG. 19 is separately provided in each of the printing units 9-1 to 9-4.
In the printing press having the above arrangement, the ink 2 in the ink fountain 1 is supplied to the ink fountain roller 3 by adjusting the opening amount of the ink fountain keys 4. The ink supplied to the ink fountain roller 3 is supplied to the plate 7 through the ink roller group 6 by the ducting operation of the ink ductor roller 5. A print sheet supplied from a feeder is printed with the ink supplied to the plate 7.
The opening amount (present position) of the ink fountain keys 4 with respect to the ink fountain roller 3 is set by using print data created in accordance with the image area ratio or the like of each of areas, corresponding to the ink fountain keys 4, of the plate 7 with reference to the home position (fully open or fully closed position) of the ink fountain keys 4 stored in advance. In this case, if printing is performed over a long period of time, the home position of the ink fountain keys 4 changes due to various reasons.
When the home position of the ink fountain keys 4 changes, the actual opening amount of the ink fountain keys 4 also changes, and a correct ink amount cannot be supplied to the plate 7. Then, the color tone of the printing product becomes largely different from a desired one, making it very difficult to obtain a printing product having a desired color tone.
Conventionally, the home position and present position of the ink fountain keys 4 are adjusted by the operator by measuring the ink thickness on the ink fountain roller 3 with a measurement unit or confirming the ink color.
In this adjusting method, the home position and present position of the ink fountain keys 4 are adjusted while measuring the ink thickness or visually confirming the ink color. This adjusting method is accordingly very difficult and takes a long period of time.
It is an object of the present invention to provide a position correcting method and apparatus for an ink fountain key, which can adjust the home position/present position of the ink fountain key easily within a short period of time.
In order to achieve the above object, according to the present invention, there is provided a method of correcting a position of an ink fountain key in a printing press, in which an amount of ink to be supplied is adjusted by adjusting a position of each of a plurality of ink fountain keys with reference to a home position, comprising the steps of setting a position of the ink fountain key as a present position with reference to the home position by using print data including an image area ratio of a reference plate having a predetermined image, printing a printing product by using the reference plate with the ink fountain key being set at the present position, measuring a density of each of respective areas, corresponding to the ink fountain keys, of the obtained printing product and correcting one of the home position and the present position of the ink fountain key on the basis of a difference between the measured density of a corresponding area and a reference density stored in advance.